1. Field of the Invention
The present invention relates to a process for synthesis of vinyl esters from butene oligomers, especially from dibutene and tributene, as well as the use of these vinyl esters.
2. Background of the Invention
Vinyl esters of tertiary carboxylic acids have long had a firm place in technology as comonomers, especially as internal plasticizers for the synthesis of environmentally safe, water-dispersable lacquers and inks on the basis of vinyl acetate. In addition to the action as plasticizers, they endow the copolymers with further advantageous properties such as high stability toward saponification, making the copolymers suitable for use under harsh conditions. Examples of such applications are as outdoor paints and thermally insulating surfacings of buildings.
The plasticizing properties of the vinyl esters, especially of tertiary carboxylic acids, depend on their chain length and on the type and position of the branches. One measure for the internal plasticization of copolymers is the glass transition temperature of the corresponding homopolymer. A comparison of the plasticizing properties of vinyl esters of various chain lengths by means of the glass transition temperature T.sub.g of the respective homopolymer reveals how it depends on molecular weight and on the degree of branching:
Glass transition Glass transition Chain length of Straight-chain temperature Tertiary vinyl temperature the carboxylic acid vinyl ester [.degree. C.] ester [.degree. C.] C.sub.2 vinyl ester Vinyl acetate +38 (33)* C.sub.3 vinyl ester Vinyl propionate -7 (-7)* C.sub.4 vinyl ester Vinyl butyrate -5 C.sub.5 vinyl ester -15*** 2,2-Dimethyl- 86 (70)* propanoic acid C.sub.6 vinyl ester Vinyl hexanoate -20 2,2-Dimethyl- 41*** butanoic acid C.sub.10 vinyl ester Vinyl decanoate -60 C.sub.12 vinyl ester Vinyl laurate -75 (-53)* (Encyclopedia of Polymer Science and Engineering, Vol. 17, p. 439 (1989), J. Wiley & Sons, Inc.), (*Ullman's Encyclopedia of Industrial Chemistry, Vol. A22, p. 2, 5.sup.th Ed. (1993), Verlag Chemie), (**C. E. L. Feeder, Surface Coatings Austral. 228, 1985), 8, pp. 11-16, (***measured by applicants).
These values are suitable only as data for comparison with one another, since they can vary with the method of synthesis of the test compound and with the test method. Nevertheless, it is evident that the plasticizing properties improve with increasing chain length of the vinyl ester (up to an alkyl group containing 12 carbon atoms in the case of straight chains). In particular, the vinyl esters of straight-chain carboxylic acids have very good plasticizing properties, but because they can be readily saponified they are not very suitable for many applications.
In contrast, the vinyl esters of tertiary carboxylic acids can be used for diverse purposes, since they are extremely stable to saponification, temperature and oxidation. On the other hand, the tertiary branch drastically reduces the plasticizing effect, and further branches in the chain lead to further deterioration, as the following examples of homopolymers of vinyl esters of tertiary C.sub.9 carboxylic acids show:
 Glass transition temperature Tertiary C.sub.9 carboxylic acids (.degree. C.) 2,3-Dimethyl-2-isopropylbutanoic acid 119 2-Ethyl-2,3,3-trimethylbutanoic acid 115 2,2,3,3-Tetramethylpentanoic acid 91 (VeoVa .RTM. 9, Shell) .sup. 70 (60)* 2,4,4-Tetramethylpentanoic acid 55 2,2,4-Trimethylhexanoic acid 10 (H. P. H. Scholten, J. Vermeulen, W. J. van Westrenen, Recent development in latices based on vinyl esters of branched monocarboxylic acids, 7th International Conference on "Water-Borne Coatings", 26-28 October 1998, Penta Hotel, London), (*W. Lau, VeoVa .RTM., Vinyl Ester Monomer Polymers DotCom Magazine, Vol. 2, No. 2, Feb. 1996).
The compounds most commonly used in modern industry are vinyl esters synthesized from a mixture of tertiary C.sub.10 carboxylic acid isomers, which form homopolymers having a glass transition temperature of -3.degree. C. As an example, this mixture is highly suitable for use and is in great demand as an internal plasticizer for polyvinyl acetate, in which it simultaneously increases the stability toward saponification.
The C.sub.10 carboxylic acid used for synthesis of the vinyl ester is in turn synthesized by addition of carbon monoxide and water to tripropene under pressure and catalysis with extremely acid catalysts (hydrocarboxylation, especially by the Koch reaction).
Tripropene, finally, a mixture of isomeric C.sub.9 olefins, is obtained in a mixture with other olefin fractions (C.sub.6, C.sub.12 and C.sub.15 olefins by acid-catalyzed oligomerization of propene). Examples of suitable catalysts for this purpose are acid zeolites or phosphoric acid on a solid support.
One disadvantage in the process for synthesis of vinyl esters of C.sub.10 carboxylic acids is that propene represents a relatively expensive raw material. Furthermore, considerable losses of raw material can be expected as a result of byproduct formation in the acid-catalyzed oligomerization of propene. Finally, it must be pointed out that the number of isomers in the tripropene fraction of the oligomer is already so large that even analytical control is difficult. The conversion to carboxylic acids ultimately leads to such a large number of isomers that it is difficult to define the properties of the resulting product mixture.
Some vinyl esters of tertiary carboxylic acids with more than 10 C atoms have been studied (for example, WO 93/22353). Certainly they all have plasticizing ability, as can be expected from their relatively long carbon chain. On the one hand, however, the necessary raw materials are in many cases not available in sufficient quantities at a reasonable price and, on the other hand, incompatibility in the copolymer becomes progressively worse with increasing chain length.
Some vinyl esters of tertiary carboxylic acids with fewer than 10 C atoms are also known and have been studied with regard to their suitability as plasticizers. For example, the vinyl esters based on pivalic acid (a tertiary C, acid) and on tertiary C.sub.9 acids (VeoVa.RTM. 9) have a certain industrial importance, but in both cases they represent comonomers having a hardening effect compared with vinyl acetate.
It would therefore be desirable to exploit raw material sources other than propene or its oligomers for the synthesis of vinyl esters which have plasticizing properties equal to or better than those of the vinyl esters of, for example, the C.sub.10 carboxylic acids based on tripropene.